1) Field of the Invention
The present invention relates to a technology for traction positional control for a motorized traction mechanism.
2) Description of the Related Art
A motorized traction mechanism for hauling a traction member such as a wire by operating a driving unit such as a motor, as in a motorized endoscope or a robot hand, to bend or rotate a distal tip is widely known. Since the motorized traction mechanism can be provided in such a manner that a generally large and heavy driving unit is separated from the distal tip via the traction member, there is a merit that the distal tip can be reduced in size and weight.
In the motorized traction mechanism, however, if the traction member in a bending or rotating state becomes loose, the distal tip does not respond until a slack is removed from the traction member.
A conventional endoscope that controls the slack of the wire is disclosed in, for example, Japanese Patent Application Laid-open No. 2000-300511. The conventional endoscope includes a flexible tube, a wire disposed in the flexible tube, a driving unit that drives the wire to for bend the flexible tube, a displacement detecting unit that detects a displacement from a reference position of the wire, a displacement direction detecting unit that detects a displacement direction of the wire, and a slack control Unit that controls the slack of the wire based on outputs of the displacement detecting unit and the displacement direction detecting unit. The conventional endoscope further includes a tension detecting unit that detects tension of the wire, and the slack control unit controls the slack of the wire based on outputs of the tension detecting unit, the displacement detecting unit and the displacement direction detecting unit.
In the conventional endoscope, a state of the slack is estimated based on displacement information and displacement direction information, and tension of wire detected by the tension detecting unit. In addition, the above publication discloses, as a concrete method for controlling the slack, that when the driving unit is driven to bend the flexible tube from an initial state (neutral reference position) in which both wire do not have the slack and any portion is not bent, one of the wire that is pushed out becomes loose, and when the driving unit is inverted and driven, assuming that the flexible tube can not be straightly bent by the loosened wire, a driving speed of the driving unit after the inversion is accelerated immediately after the inversion, and the speed is returned to the normal speed later.
However, in the conventional technology, there is no disclosure of controlling slack of the wire in a neutral reference position in the apparatus for traction positional control including both wires having the slack in the neutral reference position and characteristics that a flexible tube or wire tries to restore to an original state from a bent state.
Generally, when a distal bending section of an endoscope is operated, as described in Japanese Patent Publication No. S63-59329, a wire that is connected to the distal bending section is hauled by a driving force of an electric motor, thereby bending the distal bending section in vertical/lateral direction. When driving the electric motor, a voltage is applied to the motor in proportion to an operation amount of an operating lever provided on an operating section. In this case, by hauling the wire and moving the distal bending section vertically or laterally, a bending angle of the distal bending section can be set.
According to the conventional technology, the operation amount is determined based on a distortion gage mounted on the operating lever, and the voltage is directly applied to the motor in accordance with the operation amount. Therefore, although the electric motor can be driven in proportion to the operation amount of the operating lever, friction between the wire and an inner surface of a coil sheath for guiding the wire, and a slack of the wire are not sufficiently taken into account, the operation amount and a bending amount of the distal bending section do not correspond to each other, which is not sufficient for enhancing the operability of an observer (operator of the endoscope).
Japanese Patent Application Laid-open No. H6-22904 describes a technique in which a hauling wire is mounted to a distal bending section of an endoscope inserting portion, the hauling wire is allowed to pass through a universal cord through a relay pulley provided on the operating section, and the hauling wire is hauled by a driving force of the electric motor. It also discloses a technique in which a rotation angle of the pulley and a rotation angle of the electric motor are compared with each other, a loose state of the hauling wire is detected, and when the hauling wire is in a loosened state, the electric motor is driven at a maximum speed, and the slack of the hauling wire is instantaneously resolved.
In this conventional technology, the slack of wire generated in the universal cord between the motor and the relay pulley can be resolved, but slack and friction generated in the hauling wire of the endoscope inserting portion from the relay pulley are not taken into account, and a situation when the relay pulley does not exist is not taken into account, either.